Mexican soldiers have discovered the start of a secret underground tunnel they believe was being built as a passageway into the U.S. But it isn't just any tunnel: This one begins in a closet inside a house near Tijuana, Mexico, where a ladder dives 66 feet underground into the passageway that spans 500 feet in length.

Mexican officials said Tuesday that the path was still being constructed when it was discovered and that it didn't reach the U.S. border. However, officials believe had they not made the discovery when they did the tunnel would have eventually come out in California, about 22 miles from San Diego, the Daily Mail reported.

AUTHORITIES captured drug smugglers inside this tunnel in Mexico, but… http://t.co/lgeHOW4i3lhttp://t.co/XWoGt4wBf7

— Gboru Markson (@GboruM) April 8, 2015

Accessed through a closet, this drug smuggling tunnel was uncovered in Mexico. http://t.co/w1uuUkX12i via @RT_compic.twitter.com/JeD5Ewg9aP

— Matt Young (@MattYoung) April 8, 2015

Mexico: Tunnel being dug towards US found http://t.co/WB7it4NxmApic.twitter.com/BomO3ndcFt

— amarilloglobe (@amarilloglobe) April 8, 2015

Officials found the passageway still unfinished, although it was wired with lights and ventilation. The discovered entrance is close to a Mexican air force facility as well as a regional hub for federal police. Mexican officials said they found 44 pounds of marijuana inside the tunnel in addition to a truck that was apparently being used to expand the tunnel's length.

Altogether, nine people were arrested and the truck was impounded, Reuters reported.

In the past 10 years, dozens of illegal passageways from the U.S. to Mexico, used to smuggle illegal immigrants, have been shut down. It isn't clear how many of those tunnels were still under construction at the time of their discovery or how many were completed.

You can see more of the secret tunnel by watching the video below:

(H/T: Daily Mail)

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